1. Field of the Invention
The present invention relates to a novel process for producing aromatic hydrocarbons. More particularly, it relates to a process for efficiently producing aromatic hydrocarbons from hydrocarbons having 2 to 12 carbon atoms, particularly from aliphatic hydrocarbons having 2 to 12 carbon atoms by bringing them into contact with a modified crystalline galloaluminosilicate prepared by a specific treatment.
2. Description of the Related Arts
Zeolite catalysts of various kinds have heretofore been industrially very useful catalysts because they show high activities to catalytic rearrangement reactions of organic compounds. Particularly, crystalline silicates containing gallium have been known to exhibit excellent catalytic activity in the production of aromatic hydrocarbons from various hydrocarbon materials, such as hydrocarbons having 2 to 12 carbon atoms. Therefore, many processes for preparation and modification of the catalysts of this kind have been proposed.
For example, a process for production of aromatic hydrocarbons from a hydrocarbon material having 2 to 4 carbon atoms by bringing the material into contact with a crystalline galloaluminosilicate catalyst modified with steam is disclosed in PCT Japanese Application Laid-Open No. 501357/1985. However, this process has problems that yield of the aromatic hydrocarbons is low and that catalyst life is short.
As another example, a process for production of aromatic hydrocarbons from an aliphatic hydrocarbon material containing 50% or more of paraffins having 2 to 4 carbon atoms by bringing the material into contact with a catalyst prepared from a crystalline siliceous gallium having a mol ratio of SiO.sub.2 /Ga.sub.2 O.sub.3 in the range from 25 to 250 and a mol ratio of Y.sub.2 O.sub.3 /Ga.sub.2 O.sub.3 of less than I (Y is an atom like Al, Fe, Co, Cr and the like) by adsorption of 0.1 to 5 weight % of cokes on the catalyst, followed by a treatment of contact with gas containing oxygen at a temperature of 350.degree. to 700.degree. C., without repeating or with repeating of these treatments up to several times, is disclosed in Japanese Patent Application Laid-Open No. 98022/1984. However, this process has problems that a multi-stage treatment is required for the preparation of the catalyst and the operation of the preparation is complicated, that yield of the aromatic hydrocarbons is insufficient and that catalyst life is not satisfying.
As still another example, a process for production of aromatic hydrocarbons from a hydrocarbon material having 2 to 12 carbon atoms by bringing the material into contact with a crystalline galloaluminosilicate catalyst calcined at a high temperature of 700.degree. to 1000.degree. C. is proposed in Japanese Patent Application Laid-Open No. 103916/1989. However, this process requires a high temperature of 700.degree. C. or more for the preparation of the catalyst and is not desirable because of the higher cost of the catalyst preparation.